The present invention relates to a method for concurrently producing a copper powder and a chloride of a metal other than copper. More particularly, the invention relates to a method for concurrently producing a copper powder and a chloride of a metal other than copper such as manganese, zinc, cobalt, nickel and tin from an aqueous waste solution containing copper (II) chloride dissolved therein.
Along with the rapid progress of electronic industry in recent years, production of electronic instruments is expanding year by year while these electronic instruments are mostly assembled by arranging various kinds of electronic devices on a printed circuit board and building them into a circuit by connecting through the circuit pattern thus to construct an electronic working unit. Those printed circuit boards, hereinafter referred to as PCBs, are manufactured mostly by a process involving the step of pattern-wise etching of a copper foil adhesively bonded to the surface of an insulating substrate plate. The etching solution used for this purpose is an aqueous solution of copper (II) chloride acidified with hydrochloric acid while the depleted etching solution after use, having a specific gravity of about 1.25 and a pH value of 1 or below, usually contains, per liter of the solution, copper value in an amount of about 121 g as copper element and the overall chlorine value in an amount of about 241 g, of which about 106 g are as the chlorine ions of the hydrochloric acid, the remainder being as the counteranions of the copper (II) cations.
Such a strongly acidic waste solution containing a substantial amount of copper (II) chloride produced in a great volume in proportion to the production of PCBs of course cannot be discarded or disposed as a waste material not only from the standpoint of economy to justify recovery of at least the copper value but also from the standpoint of environmental pollution when a large volume of such a waste solution is released to public water systems. Accordingly, several methods have been proposed and practically undertaken for the recovery of copper value from such a waste solution including following three methods.
The first of the three methods is a substitution method in which the copper ions are replaced and fixed as a meal by the addition of a powder of iron as proposed in Japanese Patent Kokai 60-34501 and 63-33584 and a powder of aluminum as proposed in Japanese Patent Publication 63-14883. Namely, the copper ions are replaced with the ions of iron or aluminum and precipitated in the form of a powder which is recovered and purified to be utilized as metallic copper. The aqueous solution of iron chloride formed by the ion-substitution reaction above mentioned can be used partly as an etching solution or mostly as an inorganic floccurant in water treatment while the aqueous solution containing aluminum ions is utilized as a starting material for the manufacture of aluminum polychloride also useful as a flocculant.
The second of the three methods is a so-called neutralization method in which the waste solution is neutralized by the addition of sodium hydroxide so that the copper value is precipitated in the form of copper (II) hydroxide which is collected and subjected to a heating and dehydration treatment to be converted into copper (II) oxide. Alternatively, the copper (II) ions in the waste solution are first reduced with a copper powder into copper (I) ions followed by the neutralization with sodium hydroxide so as to be converted into copper (I) hydroxide which is collected and dehydrated into copper (I) oxide. Copper (II) oxide is utilizable as an ingredient in various kinds of ceramic materials including ferrites and the copper (I) oxide is used as a fouling-preventive pigment in ship-bottom paints.
The third of the three methods is an electrolytic method as proposed in Japanese Patent Kokai 60-128271, according to which, for example, the waste solution as such is electrolyzed by using an anion-exchange membrane to produce metallic copper and chlorine gas.
The above described three methods for the disposal of the waste solution containing a copper value each have a problem or limitation as an industrial method. For example, the substitution method has a problem in respect of the limited demand for the iron chloride or aluminum chloride produced as a by-product of the method. While these by-product chlorides have an application as a floccurant in water treatment or disposal of municipal sewage or industrial waste water, these inorganic flocculants in water treatment are under continuous replacement in recent years with flocculants based on an organic polymer so that no further increase can be expected in the demand for these inorganic flocculants, much less, to balance the rapidly increasing production of the waste solution in parallel with the increase in the production of PCBs. Accordingly, a serious problem of environmental pollution is foreseen if the only method relied on for the disposal of the waste solution is this substitution method. The neutralization method to produce oxides of copper is inherently not practicable in a large scale due to the problem in the disposal of the salt-containing waste solution produced in large volumes. Further, the electrolytic method is hardly feasible as an economical industrial process because of the quite large consumption of electric power.